Gasket having centering features

ABSTRACT

A gasket having centering features. The gasket comprises a centering portion for which three embodiments are described. The centering portion is switchable between a flush configuration, in which the gasket may be employed between the flange faces of two pipe flanges as typical, and a centering configuration, in which the gasket provides a means for centering the gasket in the pipe joint. In a first embodiment, a normally flush centering portion comprises a flap for centering the gasket, in a second embodiment, the centering portion comprises a collapsible protuberance for centering the gasket, in a third embodiment, the gasket comprises a non-collapsible protuberance for centering the gasket which is physically removable, and in a fourth embodiment the centering portion comprises an annular ring adapted for mating with an annular relief formed in a corresponding one of the flange faces.

BACKGROUND OF THE INVENTION

This invention relates to gaskets for the joinder of pipes, particularly to features provided in Such a gasket for centering the gasket in a flanged pipe joint.

It is well known to be desirable, in fluid piping systems, to provide a smooth fluid path. Non-smooth surfaces increase flow resistance and trap fluid and particulate matter which would otherwise be easily flushed out of the system. This is particularly important when carrying ultrapure materials. Protrusions and recesses alike trap bacteria or contaminants which may be released unexpectedly and undesirably at later times. In ultra-pure piping systems, contaminants in the parts per billion range may be unacceptable. Such low levels of contamination generally require extremely small surface irregularities in pipe. Concern for this can be so great that, for example, the piping pore size may be regularly inspected using scanning electron microscopy and the pipe joint rejected if the pore size is greater than a maximum allowable value. On account of the fitting together of two different sections of pipe, however, the pipe joint makes an important contribution to the problem of contaminant trapping. Moreover, the quality of this fitting cannot easily be inspected.

In particular, sections of pipe are joined with gaskets. This is because pipe flanges are formed of relatively rigid materials so that they may carry tightening forces. Pipe flange surfaces are not completely smooth or flat, and pipes are not perfectly aligned. Therefore, pipe flanges may not generally be joined in a leak-proof manner without the aid of the relatively compliant, mediating gasket. Within limits, the gasket conforms to the surface quality and angular presentation of the flange surfaces to accommodate any mis-match therebetween, to seal them.

The gasket ideally has an aperture conforming to the inner periphery of the pipe flanges, and extends radially outwardly along the interior surfaces of the pipe flanges. Typical prior art gaskets include holes through which bolts for tightening the joint are passed. The holes are larger than the bolts to ease their installation. However, the holes also provide for locating the gasket with respect to the inner periphery of the pipe flanges. It is not possible, therefore, to position the aperture to be precisely congruent with the inner periphery of the flanges.

The aperture is, typically, made “on-size”, i.e., so that the diameter of the aperture is about equal to the diameter of the inner periphery of the flanges. Since registration of the aperture with the inner periphery of the flanges is not perfect, however, the gasket generally protrudes into the stream of fluid flow in some places, and recesses from the inner surfaces of the pipe flanges in other places. Moreover, such traps cannot be avoided by making the gasket over or under-sized.

Accordingly, there is a need for a gasket having centering features that provide for improved centering the gasket in a flanged pipe joint, to decrease flow resistance and the propensity to trap fluid and particulate matter.

SUMMARY OF THE INVENTION

The present invention solves the aforementioned problems and meets the aforementioned need by providing, for use in a pipe joint comprising two pipe flanges, each pipe flange being defined by an outer diameter and an inner diameter, and including respective flange faces, outer peripheral surfaces, and inner peripheral surfaces for conducting fluid through the joint, a gasket having centering features adapted for placement of the gasket between the flange faces.

The gasket includes one or more centering portions for centering the gasket radially between the faces of the pipe flange. The centering portions are generally switchable between two configurations: a flush configuration and a centering configuration. The flush configuration permits selecting centering portions for non-use where such centering portions correspond to a size of pipe flange for which the gasket is not being employed.

The centering portions include associated centering edges adapted for making contact with the outer peripheral surface of a selected one of the flanges. The gasket is moved radially between the flange faces until the centering edge of the centering portion abuts the outer peripheral surface. The centering portion is pre-positioned for a given outer diameter of the pipe flange for centering the gasket along an associated radial line.

In a first embodiment of the invention, the centering portion includes a flap element which normally lies flush with the gasket. The flap element can be pressed out of the plane of the gasket to ready the associated centering edge for contact with the pipe flange. In a second embodiment of the invention, the centering portion includes a protuberance which extends from one side of the gasket. The protuberance contains an associated centering edge on a side thereof. The centering portion also includes a cavity in the other side of the gasket which is associated with the protuberance so that pressing the protuberance into the plane of the gasket and into the cavity places the centering portion in its flush configuration, wherein the protuberance becomes substantially flush with the gasket. In a third embodiment of the invention, the centering portion includes a protuberance which extends from one or both sides of the gasket. Removing the protuberance from the gasket places the centering portion in its flush configuration. In a fourth embodiment of the invention, the centering portion comprises an annular ring adapted for mating with an annular relief formed in a corresponding one of the flange faces.

Accordingly, it is a principal object of the present invention to provide a novel gasket having centering features.

It is another object of the present invention to provide such a gasket that decreases flow resistance and the propensity to trap fluid and particulate matter.

It is still another object of the present invention to provide such a gasket that provides for improved centering of a gasket in a flanged pipe joint.

It is yet another object of the present invention to provide such a gasket that provides for adjustment to accommodate different sizes of pipe flanges.

The foregoing and other objects, features and advantages of the invention will be more readily understood upon consideration of the following detailed description of the invention, taken in conjunction with the following drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a first embodiment of a gasket having centering features according to the present invention.

FIG. 2A is s a cross-section of a pipe joint employing the gasket of FIG. 1 with a centering portion according to the present invention in a flush configuration.

FIG. 2B is a cross-section of the pipe joint and gasket of FIG. 2A with the centering portion in a centering configuration.

FIG. 3 is a plan view of a second embodiment of a gasket having centering features according to the present invention.

FIG. 4 is a cross-section of a pipe joint employing the gasket of FIG. 3 with a centering portion according to the present invention in a centering configuration and another such centering portion in a flush configuration.

FIG. 5 a plan view of a third embodiment of a gasket having centering features according to the present invention.

FIG. 6A is a cross-section of a pipe joint employing the gasket of FIG. 5 with a centering portion according to the present invention in a centering configuration and another such centering portion in a flush configuration.

FIG. 6B is a pictorial view of a method for removing a centering portion of FIG. 6A.

FIG. 7A is a generalized gasket showing areas of reduced thickness for use in a gasket having centering features according to the present invention.

FIG. 7B is a cross-section of the gasket of FIG. 7A.

FIG. 8 is a cross-section of a pipe joint employing a fourth embodiment of a gasket having centering features according to the present invention.

FIG. 9 is a cross-section of a pipe joint employing a fifth embodiment of a gasket having centering features according to the present invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

A gasket having centering features 10 according to the present invention is particularly adapted for use with plastic pipe systems; however, the present invention may be employed to advantage as well in metal or ceramic piping systems. One example of the gasket 10 is shown in FIG. 1. The gasket 10 has an inner diameter 17 and an outer diameter 19 with respect to a center-point “C”. The dimensions of the diameters 17 and 19 are determined in consideration of the sizes of pipes and pipe flanges which are to be joined.

Referring to FIG. 2A, a typical pipe joint 11 is shown in cross-section. The joint includes pipe sections 12 a, 12 b, and flanges 14 a, 14 b. The typically cylindrical flanges 14 a, 14 b are defined by outer diameters 13 a, 13 b and inner diameters 15 a, 15 b. The flanges include respective flange faces 16 a, 16 b, outer peripheral surfaces 18 a, 18 b and inner peripheral surfaces 20 a, 20 b for conducting fluid through the joint 11. It is an outstanding feature of the present invention to accommodate any combination of dimensions of the pipe sections and flanges.

The gasket is adapted for placement between the flange faces 16 a, 16 b. The gasket includes an annular region 22 having sides 26 and 28 that make contact with the flange faces. As a result, an inner peripheral surface 20 c of the gasket is placed between the inner peripheral surfaces 20 a and 20 b of the flanges. Therefore, it is preferable that the inner diameter 15 a of the flange 14 a is substantially equal to the inner diameter 15 b of the flange 14 b and the inner diameter 17 of the gasket. This permits a diametric continuity to be maintained across the pipe joint 11 for minimizing flow restriction and trapping, to the extent that the gasket is centered in the joint.

Notwithstanding, it is an outstanding feature of the present invention to accommodate pipe flanges having any combination of sizes of inner and outer diameters, the Figures reflecting particular combinations for illustrative purposes only.

The flanges 14 a, 14 b may be joined in the typical manner, with bolts passing through apertures in the flanges, or may be joined with bolts passing through a backing ring and directing mechanism, such as the backing mechanism 8 and directing mechanism 9, for directing and focusing the tightening load toward the inner periphery of the joint surface of the flange, which also decreases the propensity for trapping fluids and particulates, as taught in the inventor's U.S. patent application Ser. No. 08/344,881, incorporated by reference herein in its entirety.

The gasket generally includes one or more centering portions 24 for centering the gasket transversely between the faces 16 a, 16 b. The centering portions are provided in the annular region 22 of the gasket. Preferably, a plurality of centering portions are provided at distinct, predetermined radial distances on the gasket, such as “r₁” and “r₂” as shown in FIGS. 3 and 5, for centering an associated plurality of different sized pipe flanges. Also preferably, there are at least three centering portions at any particular radial distance, such as “r₁”, corresponding to a particular size of pipe flange outer diameter. This permits centering the gasket in all radial directions. The centering portions may be included on either or both sides 26, 28 of the gasket.

The centering portions are generally switchable between two configurations; a flush configuration and a centering configuration. The flush configuration permits selecting particular centering portions for non-use where such centering portions correspond to a size of pipe flange for which the gasket is not being employed.

Referring particularly to the embodiment of FIGS. 1, 2A and 2B, the centering portion 24 includes at least one flap element 23. The annular region 22 has a predetermined thickness t_(a) defined by the distance between the sides 26 and 28, and the centering portion has a predetermined thickness “t_(c)” defined by the distance between a first side 30 and a second side 32 of the flap element 23. Preferably, the predetermined thickness of the centering portion is equal to or less than the predetermined thickness “t_(a)” of the annular region, so that a flush configuration of the flap element is optimally provided. Notwithstanding, a thickness “t_(c)” that is greater than or less than the thickness of the annular region may be employed without departing from the principles of the invention.

The sides 30 and 32 of the flap element terminate at a centering edge 34. The centering edge is adapted to make contact with the outer periphery of a selected one of the pipe flanges. The edge 34 is shown in FIG. 1 as having a shape following a circle centered at “C”; however, it will be understood that the centering edge 34 of this and other embodiments of the invention may have shapes that differ from those described, may be of any length, and may comprise or consist of a single point of centering contact without departing from the principles of the invention.

The flap element 23 is hingedly connected to the annular region 22. Preferably, the flap element is formed out of the annular region by scoring three sides 36 a, 36 b and 36 c thereof, wherein the side 36 b forms the centering edge 34, leaving the flap element connected to the annular region by a natural hinge 36 d. The centering portion is thereby normally in a flush configuration in which the centering portion lies flush with the annular region.

The flap element 23 may employ sides 36 a, 36 c that differ in length, to leave a centering edge 33 in addition to the centering edge 34 in the same flap element 23, for accommodating with the same flap element larger diameter pipe flanges than can be accommodated with the edge 34. The flap element is for this purpose relieved by a relief aperture 35 and slit 37 which permits bending the edge 34 with respect to the edge 33. For example, the edge 34 may be bent out of the way of a larger pipe flange so that the gasket may be located with respect to the pipe flange with the edge 33 rather than with the edge 34. Alternatively, the edge 34 may be adapted to center on the flange 14 a while the edge 33 is adapted to center on the flange 14 b. In similar manner, any number of additional centering edges at different radial distances, and their associated relief apertures, may be provided as will be readily apparent.

The centering portion may be adjusted between the flush configuration, in which the centering portion does not protrude substantially beyond the first and second sides 26, 28 of the annular region 22, and a centering configuration, shown in FIG. 2B, in which the centering portion is pivoted away from the general plane of the gasket so that the centering edge 34 protrudes beyond a selected one of the first and second sides 26, 28 of the annular region.

As shown particularly in FIG. 1, the gasket 10 may include other features, such as notches 112 for receiving a thickness gauge as taught in the inventor's International Application, No. PCT/US94/08087, Publication No. WO/9602787, herein incorporated by reference in its entirety, and apertures 25 for receiving bolts wherein the outer diameter of the gasket is appropriately sized relative to the outer diameters of the flanges for this purpose. It should be noted in connection with the former that the aforedescribed relief aperture 35 also provides a recess for receiving a thickness gage.

Turning now to FIGS. 3 and 4, in a second embodiment of a gasket 10 according to the present invention, the centering portion 24 includes an axially extending, collapsible protuberance 40 and associated, preferably axially co-linear, cavity 42. The centering portion 24 has a predetermined thickness “t_(c)” defined by the bottom 43 of the cavity and the top 45 of the protuberance. Preferably, the predetermined thickness of the centering portion is equal to the predetermined thickness “t_(a)” of the annular region. The protuberance includes a centering edge 34 on a side thereof.

The centering portion 24 is normally in a centering configuration, in which the collapsible protuberance 40 protrudes axially from a selected one of the first and second sides of the annular region. The centering portion may be caused to adopt a flush configuration, in which the collapsible protuberance lies flush with the annular region 22 and does not protrude substantially beyond the first and second sides 26, 28 thereof. For example, the bulk of the collapsible protuberance 40 may be accommodated by the cavity 42 in response to pressing the collapsible protuberance toward the cavity. In FIG. 4, one protuberance 40 a is shown in its flush configuration and another protuberance 40 b is shown in its centering configuration.

Turning now to FIGS. 5 and 6A, in a third embodiment of the gasket, the centering portion includes a one or more axially extending removable protuberances 50 that extend axially outwardly from the sides 26, 28 of the annular region. Each of the removable protuberances 50 includes corresponding centering edges 54 on associated sides thereof

The centering portion 24 is normally in a centering configuration, in which at least one of the removable protuberances 50 protrudes axially from selected of the first and second sides of the annular region. The centering portion may be caused to adopt a flush configuration in which one or more of the removable protuberances lie flush with the annular region 22 and do not protrude substantially beyond the first and second sides 26, 28 thereof, by physically removing the protuberance, such as by cutting the protuberance substantially flush with the associated side of the annular region. Referring to FIG. 6B, a knife 60 may be used for this purpose, as shown, whereas in FIG. 6A the remnant of a protuberance 50a that has been removed is indicated.

To permit centering any of the aforedescribed embodiments of the gasket about a selected one of the pipe flanges 12 a, 12 b, e.g., the flange 12 a, the outer diameter 19 of the gasket and the radial locations of the centering portion 24, such as “r₁” and “r₂” of FIG. 3, are pre-selected in consideration of the dimensions of the flange 14 a. Specifically, the outer diameter 19 of the gasket is selected to be sufficiently larger than the outer diameter 13 a of the pipe flange to permit the centering portion 24 to be disposed outside of the pipe flange. In cooperation, the centering edge is positioned to be substantially congruent with the outer peripheral surface 18 a of the flange when the gasket is centered as desired.

For centering the aforedescribed embodiments of the gasket 10 in the pipe joint 11, the centering portion 24 is caused to adopt, if it is not already in, its centering configuration. With exemplary reference to FIG. 5, the centering edge 34 is thence permitted to contact the outer peripheral surface 18 a of a selected flange 12 a a along one or more points of contact “P” contained thereon. This locates the gasket radially along lines “L” which intersect the points “P” and the center “C” of the flange.

With exemplary reference to FIG. 4, a stiffener 55 may be employed with any of the aforedescribed embodiments and, moreover, with any prior art gasket as well, such as the gasket described in the inventor's prior U.S. Pat. No. 5,362,115 (the '115 Patent), herein incorporated by reference in its entirety. The stiffener is preferably a stainless steel wire mesh or grid which is encapsulated in a flexible, e.g., non-metallic, gasket material. The gasket material may be molded around an insert of the wire mesh, such processing being well known in the plastic molding arts. It is preferable to encapsulate the mesh in the vicinity of inner peripheral regions 70, which mediate the inner peripheral surfaces 20 a, 20 b and the flange faces 16 a, 16 b, to prevent the mesh, even though it is preferably formed of a relatively inert material, from potential damage and consequent spread of contamination due to its coming into contact with corrosive substances. Where the cavity 42 is employed, the mesh should also provide relief therefor. Otherwise, the bolt holes and other apertures through the gasket may be die-cut with the mesh in place. Notwithstanding, the mesh may be fully or partially encapsulated as desired without departing from the principles of the invention.

Turning to FIGS. 7A and 7B, it may also be preferable, particularly where bolts pass through the flanges, to include annular areas “A” of reduced thickness in the gasket 10, on portions thereof that contact the flange faces 16 a, 16 b. Centering portions are preferably provided in the outermost annular region of the regions “A”, i.e., annular region “A,”. The annular regions “A” are provided for reasons described in the '115 Patent. Particularly, as taught in the '115 Patent, it is desirable to minimize the area over which the gasket seal is made, for increasing the sealing pressure while at the same time decreasing the total force required therefor, and to place the gasket material as near as possible to points on the flanges at which tightening forces are applied, to decrease the tendency for the flanges to distort on account of the gasket's resistance to compression.

Referring to FIGS. 8 and 9, additional embodiments of the gasket 10 having centering features are depicted. These embodiments are generally characterized by the employment, in registering the gasket 10 to the flanges 14 a, 14 b, of protuberances that are particularly shaped for mating with corresponding reliefs provided in the flange faces 16 a, 16 bof the flanges. Significantly, the protuberances are not employed to make the gasket seal and, therefore, may be particularly adapted for centering purposes. For example, in some prior art gaskets, a relief is formed in corresponding pipe flanges for receiving all or a large portion of the gasket. When the pipe joint is tightened, the relief and the portion of the gasket in the vicinity thereof are pressed tightly together for the purpose of making the gasket seal. Where the gasket is relatively compliant, such portion must substantially deform in response to this force. This change in the dimensions of the portion upon application of tightening forces would prevent the portion from being effective for the purpose of accurately center the gasket.

In the embodiments of the invention shown in FIGS. 8 and 9, one or more annular, ringlike protuberances 78 a, 78 b are provided along the sides 26 and 28 between the outer diameter 19 and the inner diameter 17 of the gasket 10. The thickness of the gasket 10 changes from the base thickness “t₁” to the thickness “t₂” along a circumference lying between the inner diameter 17 and the outer diameter 19 of the gasket 10. The flange faces 16 a, 16 b are appropriately relieved by corresponding reliefs 80 a, 80 b, having shapes that are complementary to the shapes of the protuberances 78 a, 78 b. For example, as in FIG. 8, the protuberances may have a semi-circular cross-section, with the flange faces including annular grooves having a slightly larger semi-circular cross-section. As in FIG. 9, the protuberances may have a triangular cross-section, with the flange faces including annular grooves having a triangular cross-section. The grooves and protuberances are preferably adapted to fit together so that they do not, on the one hand, substantially interfere when the flange faces 16 a and 16 b are brought tightly together against the gasket and, on the other, are not substantially loose. Either of these conditions detracts from the capability of the centering portions for centering the gasket. Accordingly, the seal is preferably made at least primarily at sealing portions 82 of the gasket that contact substantially planar surfaces of the flange faces 16 a, 16 b rather than at the interface of the protuberances and the reliefs. It is also preferable that sealing portions 84 remain proximate the interface between the inner peripheral surfaces 20 a and 20 b of the pipe joint, to minimize flow restriction and trapping

Particular shapes of protuberances 74 a, 74 b, 78 a, 78 b having been shown, it will be readily apparent to those of ordinary skill that the protuberances may have any other cross-sectional or circumferential position-dependent shape the thickness of the gasket changes from a base level of thicknesses “t₁” to an increased thickness “t₂”. The protuberances may all have the same shapes or may have differing shapes, and the protuberances 74 a, 74 b and 78 a, 78 b may or may not be symmetrical with each other, all to provide for particular advantages. For example, it is preferable to employ pairs of protuberances mating with corresponding reliefs in both flange faces, to more positively align the entire pipe joint and to provide for interchangeable pipe sections 12 a, 12 b. However, either the protuberances having the reference designator “a” or the protuberances having the reference designator “b” in FIGS. 8 and 9 may be omitted to save the cost of forming a relief in one of the flanges. This may be particularly desirable, for example, when different sized pipe flanges are being coupled together to form the pipe joint 11, so that it is no longer an objective to provide for interchangability of the pipe sections.

It is to be recognized that, while a specific gasket having centering features has been shown as preferred, other configurations could be utilized, in addition to configurations already mentioned, without departing from the principles of the invention.

The terms and expressions which have been employed in the foregoing specification are used therein as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding equivalents of the features shown and described or portions thereof, it being recognized that the scope of the invention is defined and limited only by the claims that follow. 

I claim:
 1. A pipe joint having a first flange and a second flange, each flange including a flange face and an outer peripheral surface, the pipe joint comprising a gasket formed of a relatively compliant material, said gasket having first and second sides adapted for sealing between the flange faces, said gasket including at least one centering portion having a centering edge, said centering portion being adapted to protrude, in a centering configuration, from at least one of said sides at a predetermined location on said gasket so that said centering edge is positioned to contact the outer peripheral surface of at least one of the flanges and thereby register said gasket thereto.
 2. The gasket of claim 1, wherein said centering portion is switchable from a flush configuration, wherein said centering portion does not protrude from either of said sides of the gasket, to said centering configuration.
 3. The gasket of claim 2, wherein said centering portion includes a flap element having a hinged end connecting said flap element to said gasket and a free end which includes said centering edge.
 4. The gasket of claim 2, wherein said centering portion includes a protuberance protruding from one of said sides of the gasket and an associated cavity in the other of said sides, said protuberance having a side which includes said centering edge, said cavity being adapted to receive said protuberance when said protuberance is pressed toward said cavity.
 5. The gasket of claim 4, wherein said protuberance has a top surface and said cavity has a bottom surface, said protuberance and said cavity being adapted so that, when said centering portion is switched to said flush configuration, said top surface is substantially flush with one of said sides of the gasket, and said bottom surface is substantially flush with the other of said sides.
 6. The gasket of claim 2, wherein said centering portion includes a protuberance protruding from one of said sides, said protuberance having a side which includes said centering edge.
 7. The gasket of claim 1, further comprising a stiffening member contained substantially within the interior of the gasket.
 8. The gasket of claim 1, wherein said centering portion is switchable from said centering, configuration to a flush configuration wherein said centering portion does not protrude from either of said sides.
 9. The gasket of claim 8, wherein said centering portion is adapted to be removed from the gasket to produce said flush configuration.
 10. The pipe joint of claim 1, wherein said gasket has an outer diameter that is greater than the outer diameter of said at least one flange, and wherein said centering portions are adapted to protrude from the portion of said gasket that is outside the outer diameter of said at least one flange when the gasket is centered therebetween.
 11. A method for centering a gasket in a pipe joint having a first flange and a second flange, each flange including an outer peripheral surface, the gasket being formed of a relatively compliant material and having first and second sides adapted for making contact with, respectively, the flange face of the first flange and the flange face of the second flange, the method comprising forming a centering portion by scoring the gasket along first and second lines, each line being defined by an associated first point of termination and an associated second point of termination, wherein said first point of termination of said first line and said first point of termination of said second line defines a natural hinge in said gasket, wherein said second point of termination of said first line and said second point of termination of said second line defines a centering edge adapted for making contact with the outer peripheral surface of one of the first and second flanges and thereby to register the gasket with respect thereto.
 12. The method of claim 11, further comprising switching said centering portion from a first configuration wherein said centering portion does not protrude from either of the first and second sides of the gasket, to a second configuration wherein said centering portion protrudes from one of the first and second sides of the gasket.
 13. A method for preparing a gasket having a plurality of centering portions for installation in a pipe joint having a first flange and a second flange, each flange having an outer peripheral surface, the gasket being formed of a relatively compliant material and having first and second sides adapted for making contact with, respectively, the flange face of the first flange and the flange face of the second flange, wherein one or more of the centering portions becomes disposed between the flange face of the first flange and the flange face of the second flange when the gasket is installed in the pipe joint and substantially centered therein, the method comprising: providing the centering portions with means for switching the centering portions from a first configuration wherein said centering portion protrudes from one of the first and second sides of the gasket and is adapted for making contact with the outer peripheral surface of at least one of the flanges for centering the gasket with respect thereto, to a second configuration wherein said centering portion does not protrude from either of the first and second sides of the gasket; selecting the centering portions that would become disposed between the flange face of the first flange and the flange face of the second flange when the gasket is installed in the pipe joint; and manipulating the selected said centering portions so as to cause said centering portions to adopt said second configuration.
 14. The method of claim 13, further comprising the steps of providing the centering portions to include a collapsible protuberance protruding axially from the gasket and adapted to adopt said second configuration upon being pressed toward the gasket, and pressing said collapsible protuberance toward the gasket to collapse said collapsible protuberances.
 15. The method of claim 13, further comprising the steps of providing the centering portion to include a protuberance protruding axially from the gasket and cutting said protuberance substantially flush with said gasket.
 16. A gasket, comprising a sealing material having two opposite sides for sealing between respective faces of two pipe flanges, the gasket further comprising a centering portion which is switchable from a flush configuration in which said centering portion does not extend substantially beyond either of said sides, to a centering configuration in which at least a portion of said centering portion is disposed beyond at least one of said sides at a predetermined location on the gasket for centering the gasket between the pipe flanges.
 17. The gasket of claim 16, wherein said centering portion includes a flap element having a hinged end connecting said flap element to said gasket and a free end which includes said centering edge.
 18. The gasket of claim 17, including a first annular region and an adjacent second annular region having a thickness that is substantially less than the thickness of said first annular region, wherein said centering portion is disposed in said second annular region.
 19. A gasket, comprising a sealing material having two opposite sides for sealing between respective faces of two pipe flanges, the gasket further comprising a protuberance projecting outwardly from one of said sides, wherein said protuberance is elongate with an elongate axis of said protuberance substantially perpendicular to said one side.
 20. The gasket of claim 19, including a first annular region and an adjacent second annular region having a thickness that is less than the thickness of said first annular region, wherein said protuberance is disposed in said second annular region.
 21. A gasket, comprising a sealing material having two opposite sides for sealing between respective faces of two pipe flanges, the gasket further comprising a protuberance projecting outwardly from one of said sides and an associated cavity in the other of said sides, said cavity being adapted to receive said protuberance when said protuberance is pressed toward said cavity.
 22. The gasket of claim 21, wherein said protuberance is elongate with an elongate axis of said protuberance substantially perpendicular to said one side.
 23. The gasket of claim 21, including a first annular region and an adjacent second annular region having a thickness that is less than the thickness of said first annular region, wherein said protuberance is disposed in said second annular region.
 24. A pipe joint, comprising two pipe flanges and a gasket comprising a substantially flat material having two opposite sides for sealing between respective faces of the pipe flanges, said gasket further comprising a first protuberance projecting outwardly from one of said sides, said protuberance having two sides defining two respective radial distances from the center of said gasket, wherein at least one of the pipe flanges comprises a complementary recess for receiving both sides of said protuberance when the pipe joint is assembled.
 25. The pipe joint of claim 24, wherein said protuberance is annular.
 26. The gasket of claim 25, wherein said protuberance has a substantially triangular cross-section.
 27. The gasket of claim 25, wherein said protuberance has a substantially semi-circular cross-section.
 28. The pipe joint of claim 24, further comprising a second protuberance projecting outwardly from the other of said sides of the gasket, and wherein the pipe flanges each have complementary recesses for receiving said first and second protuberances respectively.
 29. A method for sealing between pipe flanges having respective flange faces and outer peripheral surfaces, the method comprising providing a gasket comprising sealing material having two opposite sides for sealing between the respective faces of the pipe flanges and a first centering portion having a centering edge disposed beyond one of said sides at a predetermined location on the gasket, and placing the gasket between the flange faces so that said centering edge is adjacent the outer peripheral surface of one of the pipe flanges, for centering the gasket between the flanges.
 30. The method of claim 29, further comprising providing a second centering portion of the gasket having a centering edge disposed or disposable beyond the other of said sides, and wherein said step of placing the gasket between the flange faces provides that said centering edge of said second centering portion is adjacent the outer peripheral surface of the other of the pipe flanges.
 31. The method of claim 29, further comprising removing said centering portion from the gasket after said step of placing the gasket between the flange faces for centering the gasket between the flanges.
 32. A method for sealing between pipe flanges having respective flange faces and outer peripheral surfaces, the method comprising providing a gasket having two opposite sides for sealing between the respective faces of the pipe flanges, the gasket comprising a first centering portion disposed in a centering configuration wherein a centering edge thereof is disposed beyond one of said sides, said first centering portion being switchable from said centering configuration to a flush configuration wherein said centering portion including said edge does not extend substantially beyond either of said sides, providing a second centering portion of the gasket disposed or disposable in a centering configuration wherein a centering edge thereof is disposed beyond one of said sides, switching said first centering portion into said flush configuration and placing the gasket between the flange faces so that said centering edge of said second centering portion is adjacent the outer peripheral surface of one of the pipe flanges..
 33. The method of claim 32, wherein said step of switching comprises cutting said first centering portion from said gasket with a knife.
 34. The method of claim 32, wherein said step of switching comprises manipulating a flap element hingedly attached to the gasket.
 35. A method for sealing between pipe flanges having respective flange faces and outer peripheral surfaces, the method comprising providing a gasket having two opposite sides for sealing between the respective faces of the pipe flanges, the gasket comprising a first centering portion disposed in a centering configuration wherein a centering edge thereof is disposed beyond one of said sides, said first centering portion being switchable from said centering configuration to a flush configuration wherein said centering portion including said edge does not extend substantially beyond either of said sides, providing a second centering portion of the gasket disposed in a centering configuration wherein a centering edge thereof is disposed beyond one of said sides, selecting one of said first and second centering portions, switching the selected said centering portion from one of the respective said configurations to the other, and placing the gasket between the flange faces so that the centering edge of the selected said centering portion is disposed adjacent one of the outer peripheral surface of one of the pipe flanges and the centering edge of the unselected said centering portion is disposed between the flange faces.
 36. The method of claim 35, wherein said step of placing places the centering edge of the selected said centering portion between the flange faces, the method further comprising switching the other of said centering portions from the respective flush configuration to the respective centering configuration, and wherein said step of placing places the centering edge of the other of said centering portions adjacent the outer peripheral surface of one of the pipe flanges.
 37. The method of claim 35, wherein said first centering portion is disposed in the respective said centering configuration and said second centering portion is disposed in the respective said centering configuration, and wherein said step of switching comprises switching one of said centering portions into the respective said flush configuration.
 38. The method of claim 37, further comprising providing one of said centering portions with an axially extending protuberance and associated cavity, wherein said step of switching includes pressing said protuberance toward said cavity so as to collapse said protuberance.
 39. The method of claim 37, further comprising providing said one of said centering portions with an axially extending protuberance, wherein said step of switching includes removing said protuberance from the gasket.
 40. The method of claim 39, wherein said step of removing includes cutting said protuberance with a knife.
 41. The method of claim 35, wherein said first centering portion is disposed in the respective said flush configuration and said second centering portion is disposed in the respective said flush configuration, and wherein said step of switching comprises switching one of said centering portions into the respective said centering configuration.
 42. The method of claim 41, further comprising providing a flap element for said one of said centering portions, said flap element having a hinged end connecting said flap element to the gasket and a free end which includes the respective said centering edge, and wherein said step of switching includes manipulating said flap element.
 43. The method of claim 35, further comprising providing a third centering portion disposed in a centering configuration wherein a centering edge of said third centering portion is disposed beyond one of said sides, and placing said centering edge of said third centering portion adjacent the outer peripheral surface of the other of the pipe flanges.
 44. The method of claim 35, further comprising providing a third centering portion disposed in a flush configuration wherein said centering edge of said third centering portion does not extend substantially beyond either of said sides, and placing said centering edge of said third centering portion between the flange faces.
 45. A gasket, comprising a sealing material having two opposite sides for sealing between respective faces of two pipe flanges, the gasket further comprising a centering portion which is switchable from a centering configuration in which said centering portion protrudes from at least one of said sides at a predetermined location on the gasket for centering the gasket between the pipe flanges to a flush configuration in which said centering portion does not extend substantially beyond either of said sides.
 46. The gasket of claim 45, wherein said centering portion is adapted to be removed from the gasket to produce said flush configuration.
 47. A method for sealing between pipe flanges having respective flange faces and outer peripheral surfaces, the method comprising providing a gasket comprising sealing material having two opposite sides for sealing between the respective faces of the pipe flanges and a first centering portion having a centering edge disposable beyond one of said sides at a predetermined location on the gasket, and placing the gasket between the flange faces so that said centering edge is adjacent the outer peripheral surface of one of the pipe flanges, for centering the gasket between the flanges.
 48. A method for sealing between pipe flanges having respective flange faces and outer peripheral surfaces, the method comprising providing a gasket having two opposite sides for sealing between the respective faces of the pipe flanges, the gasket comprising a first centering portion disposable in a centering configuration wherein a centering edge thereof is disposed beyond one of said sides, said first centering portion being switchable from said centering configuration to a flush configuration wherein said centering portion including said edge does not extend substantially beyond either of said sides, providing a second centering portion of the gasket disposable in a centering configuration wherein a centering edge thereof is disposed beyond one of said sides, selecting one of said first and second centering portions, switching the selected said centering portion from one of the respective said configurations to the other, and placing the gasket between the flange faces so that the centering edge of the selected said centering portion is disposed adjacent one of the outer peripheral surface of one of the pipe flanges and the centering edge of the unselected said centering portion is disposed between the flange faces.
 49. The method of claim 48, further comprising providing a third centering portion disposable in a centering configuration wherein a centering edge of said third centering portion is disposed beyond one of said sides, and placing said centering edge of said third centering portion adjacent the outer peripheral surface of the other of the pipe flanges.
 50. The method of claim 48, further comprising providing a third centering portion disposable in a flush configuration wherein said centering edge of said third centering portion does not extend substantially beyond either of said sides, and placing said centering edge of said third centering portion between the flange faces. 